Polypropylene resins have been widely used in various fields, such as fibers, films and other shaped articles, because of their excellent physical and mechanical properties. However, polypropylene has high crystallinity and poor affinity for dye or pigments.
Attempts have been made to improve the dye receptivity of polypropylene resin. For example, U.S. Pat. No. 3,415,904 discloses incorporating into polypropylene an ethylene/acrylic ester copolymer which has been treated with an amine. U.S. Pat. No. 4,872,880 discloses treating a polyolefin article with an aqueous dye bath, wherein the polyolefin is a blend of a polyolefin and a copolymer selected from (a) a zinc ionomer of a copolymer of an alpha-olefin and (b) a graft copolymer of at least one alpha, beta-unsaturated carboxylic acid or unsaturated carboxylic acid anhydride grafted onto a polyolefin backbone.
It is known and discussed in the paper of Y. Lin, et. al., entitled, "The Effect of Pigments on the Development of Structure and Properties of Polypropylene Filaments", ANTEC '91, page 1950-1953, that many compounds act as nucleating agents for the crystallization of polypropylene and different pigments nucleate crystallization in polypropylene during the fiber forming process, blue pigments being highly active as a nucleating agent and white pigments being substantially less active.
Thus, in view of the varying degree of nucleating activity of different pigments, when processing fibers/yarns of propylene polymer resins having color, adjustments typically must be made in processing conditions, spinning speeds and draw ratios, in order to produce colored fibers/yarns with consistent and desirable properties depending upon the particular color used. These changes in processing conditions generally result in lost production time as well as production of yarns that do not meet target specifications.